Control method for inhibiting periodic fluctuation of crystallizer liquid level in SPHC steel grade production

Abstract

The invention provides a control method for inhibiting the periodic fluctuation of the liquid level of a crystallizer in SPHC steel grade production, which is characterized in that when the SPHC steel grade is cast, low-carbon steel casting powder is used, and the depth of a submersed nozzle inserted into the liquid level of the crystallizer is 130-170mm; the pulling speed of the crystallizer is 1.0-2.0 m / min, the amplitude is 3-6 mm, and the vibration frequency is 170-150 times; wherein the treatment comprises crystallizer cooling treatment and secondary cooling treatment; when the periodic fluctuation value of the liquid level of the crystallizer is smaller than or equal to 10 mm, the cooling strength of the secondary cooling treatment is 0.8-0.9 L / kg; when the periodic fluctuation value of the liquid level of the crystallizer is greater than 10mm, the cooling strength of the secondary cooling treatment is 1.0-1.1 L / kg; by limiting the use of special casting powder for low-carbon steel during casting, the depth of the submersed nozzle inserted into the liquid level of the crystallizer, a crystallizer vibration model and a specific secondary cooling grading treatment method, the fluctuation value of the liquid level of the crystallizer can be reduced from original 10-20 mm to 3 mm or even has no fluctuation, and the technological requirements of slabs are met; and the periodic fluctuation of the liquid level of the crystallizer is effectively inhibited.

Description

Technical Field

[0001] This invention belongs to the field of continuous casting of low-carbon steel, specifically relating to a control method for suppressing periodic fluctuations in the liquid level of the crystallizer during the production of SPHC steel. Background Technology

[0002] With the continuous increase in casting speed and the constant breaking of limits for low-carbon steel, continuous casting is facing significant quality challenges, with frequent occurrences of problems such as billet bulging and fluctuations in the liquid level in the crystallizer. This is especially true for SPHC series steels, which require a carbon content of ≤0.06%. As casting speeds increase, billet bulging is more likely to cause periodic fluctuations in the liquid level in the crystallizer, significantly impacting production, quality, and costs.

[0003] Periodic fluctuations in the liquid level in the crystallizer cause slag to form on the cast billet, and peeling or black lines to appear on the surface of hot-rolled strip steel, which seriously affects the quality of the strip steel and poses a significant quality risk. Summary of the Invention

[0004] This invention provides a control method for suppressing periodic fluctuations in the liquid level of the crystallizer during the production of SPHC steel, which solves the problem of periodic fluctuations in the liquid level of the crystallizer in the production of SPHC steel in the prior art.

[0005] This invention provides a method for controlling periodic fluctuations in the liquid level of the crystallizer during the production of SPHC steel. The method is characterized by using low-carbon steel protective slag during the casting process of SPHC steel, inserting the submerged nozzle to a depth of 130-170 mm into the liquid level of the crystallizer, and using a crystallizer with a casting speed of 1.0-2.0 m / min, an amplitude of 3-6 mm, and a frequency of 170-150 Hz. This includes crystallizer cooling treatment and secondary cooling treatment; when the periodic fluctuation value of the crystallizer liquid level is ≤10mm, the cooling intensity of the secondary cooling treatment is 0.8~0.9L / kg; when the periodic fluctuation value of the crystallizer liquid level is >10mm, the cooling intensity of the secondary cooling treatment is 1.0~1.1L / kg.

[0006] Compared with the prior art, the advantages of this invention are as follows: The control method for suppressing periodic fluctuations of the liquid level in the crystallizer during the production of SPHC steel provided by this invention, by limiting the use of special protective slag for low-carbon steel during casting, the depth of the submerged nozzle inserted into the liquid level in the crystallizer, the crystallizer vibration model, and a specific secondary cooling and grading treatment method, can reduce the fluctuation value of the liquid level in the crystallizer from the original 10-20mm to 3mm or even no fluctuation, which meets the requirements of the slab process, effectively suppresses the periodic fluctuations of the liquid level in the crystallizer, improves the quality of the cast slab, and ensures the rolling quality; and under the premise of keeping the existing equipment operating conditions unchanged, the investment is small and the results are quick, making it suitable for widespread application.

[0007] Furthermore, the basicity of the low-carbon steel protective slag is 0.95±0.15, the viscosity is 0.2±0.1 Pa·S, and the moisture content is <0.5%.

[0008] Furthermore, the mass composition of the low-carbon steel protective slag includes: CaO: 28.5±5.0%, SiO2: 31.0±5.0%, Al2O3: 4.5±3.0%, F: 8.0±3.0%, Tc: 6.0±3.0%, MgO: ≤5.0%.

[0009] Furthermore, the intermediate ladle temperature is 1550~1565℃, and the carbon content is ≤0.06%.

[0010] Furthermore, in the cooling process of the crystallizer, the water flow rate on the wide side is 3100~3300L / min, and the water flow rate on the narrow side is 460~500L / min.

[0011] Furthermore, full-process protective casting is adopted, with the argon flow rate at the top nozzle of the tundish being 2.2~3.2L / min and the argon flow rate at the stopper rod being 1.0~2.5L / min.

[0012] Furthermore, the thickness of the cast section is 200~230mm, and the width is 900~1235mm.

[0013] Furthermore, an automatic control system for the liquid level in the crystallizer is adopted, wherein the initial setting value of the KP system in the PID parameters is 1.0, and the initial setting value of the TI system is 0.5.

[0014] Furthermore, the depth of the immersion nozzle inserted into the liquid surface of the crystallizer is successively increased to 130mm-150mm-170mm.

[0015] Furthermore, the liquid level in the crystallizer is automatically controlled using an eddy current probe. Attached Figure Description

[0016] Figure 1 This is a schematic diagram illustrating the principle of periodic fluctuations in the liquid level of the crystallizer caused by the bulging of the cast billet in this invention. Figure 2 This is a schematic diagram of the periodic fluctuation of the liquid level in the crystallizer in this invention; Figure 3 A schematic diagram of argon blowing casting to collect inclusions at the inlet and stopper rod; Figure 4 Here are actual casting images of the liquid level in the crystallizer during the casting process in this invention: Figure 5 Images showing periodic fluctuations in the liquid level of the crystallizer in the experimental example; Figure 6 The image shows actual slag inclusions on the surface of the billet when the liquid level in the crystallizer fluctuates periodically in the experimental example. Figure 7 The image shows actual defects on the strip surface when the liquid level in the crystallizer fluctuates periodically in the experimental example. Figure 8 This is an actual picture of the billet after it was peeled off the production line when the liquid level in the crystallizer fluctuated periodically in the test example. Figure 9 The image shows a crystallizer with no ripples in the test case. Figure 10 This is an actual image of the billet surface without defects when the liquid level in the crystallizer is stable during the test example. Figure 11 This is an actual picture of the strip surface without defects when the liquid level in the crystallizer is stable during the test example.

[0017] Explanation of reference numerals in the attached figures: 1. Roller; 2. Billet shell; 3. Nozzle; 4. Molten steel; 5. Argon gas pipe; 6. Stopper rod; 7. Crystallizer; 8. Top nozzle; 9. Submerged entry nozzle; 10. Inclusions; 11. Argon gas at the top nozzle; 12. Argon gas at the stopper rod; 13. Eddy current probe. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0019] This invention provides a method for controlling periodic fluctuations in the liquid level of the crystallizer during the production of SPHC steel. When casting SPHC steel, low-carbon steel protective slag is used, and the depth of the submerged nozzle inserted into the liquid level of the crystallizer is 130~170mm; the crystallizer casting speed is 1.0-2.0m / min, the amplitude is 3~6mm, and the frequency is 170~150 times. This includes crystallizer cooling treatment and secondary cooling treatment; when the periodic fluctuation value of the crystallizer liquid level is ≤10mm, the cooling intensity of the secondary cooling treatment is 0.8~0.9L / kg; when the periodic fluctuation value of the crystallizer liquid level is >10mm, the cooling intensity of the secondary cooling treatment is 1.0~1.1L / kg.

[0020] When performing casting treatment for SPHC steel grades, please refer to [reference needed]. Figure 1 and Figure 2 When the billet passes through roller 1, the billet shell 2 is relatively thin and cannot resist the static pressure of the molten steel 4. The billet shell 2 bulges outward, and the molten steel 4 fills inward, causing the actual liquid level in the crystallizer to drop. Upon passing through the next roller 1, the billet shell 2 is squeezed, and the actual liquid level in the crystallizer rises, ultimately forming... Figure 2 The sinusoidal periodic fluctuations in the middle.

[0021] The method for controlling periodic fluctuations in the liquid level of the crystallizer during the production of SPHC steel provided by this invention reduces the fluctuation value of the liquid level in the crystallizer from the original 10-20 mm to 3 mm or even zero fluctuation by limiting the use of special protective slag for low-carbon steel during casting, the depth of the submerged nozzle inserted into the liquid level of the crystallizer, the crystallizer vibration model, and a specific secondary cooling and grading treatment method. This meets the requirements of the slab process, effectively suppresses the periodic fluctuations of the liquid level in the crystallizer, improves the quality of the cast slab, and ensures the rolling quality. Furthermore, it requires less investment and yields quick results without changing the existing equipment operating conditions, making it suitable for widespread application.

[0022] Furthermore, the basicity of the low-carbon steel protective slag is 0.95±0.15, the viscosity is 0.2±0.1 Pa·S, and the moisture content is <0.5%.

[0023] By limiting the alkalinity, viscosity, and moisture content of the protective slag, the adsorption capacity of inclusions can be further improved, the heat transfer of the billet shell can be slowed down, the billet shell growth can be made more uniform, and the fluctuations can be further reduced.

[0024] In one specific embodiment, the main mass components of the low-carbon steel protective slag include: CaO: 28.5±5.0%, SiO2: 31.0±5.0%, Al2O3: 4.5±3.0%, F: 8.0±3.0%, Tc: 6.0±3.0%, MgO: ≤5.0%, and also include other components such as Fe2O3, Na2O, K2O, S, and unavoidable impurities.

[0025] Furthermore, the intermediate ladle temperature is 1550~1565℃, and the carbon content is ≤0.06%.

[0026] The inventors discovered that by specifically limiting the tundish temperature, it is possible to further control the crystallization process of steel, thereby improving its microstructure and final properties, and further reducing liquid level fluctuations.

[0027] Furthermore, in the cooling process of the crystallizer, the water flow rate on the wide side is 3100~3300L / min, and the water flow rate on the narrow side is 460~500L / min.

[0028] The molten steel in the crystallizer needs to be cooled rapidly by cooling water to form a solid billet shell. By further limiting the amount of cooling water on the wide and narrow sides of the crystallizer, the thickness of the billet can be further increased, the liquid surface fluctuation can be reduced, and the surface quality can be improved.

[0029] Specifically, full-process protective casting is adopted, with the argon flow rate at the top nozzle of the tundish being 2.2~3.2L / min and the argon flow rate at the stopper rod being 1.0~2.5L / min.

[0030] By adjusting the argon flow rate at the inlet and stopper, the fluctuation of the liquid level in the crystallizer can be further controlled. Using the argon flow rate defined by the above parameters can further stabilize the liquid level in the crystallizer, avoiding problems such as slag entrapment or exposed molten steel caused by excessive liquid level fluctuations. Simultaneously, adjusting the argon flow rate helps remove harmful gases and inclusions from the molten steel. The introduction of argon can make the protective slag more uniformly formed, promote the flotation and removal of non-metallic inclusions in the molten steel, and improve the cleanliness of the molten steel. It can also promptly flush away inclusions in the inlet, keeping the inlet unobstructed and further improving the quality of the cast billet.

[0031] In one specific embodiment, the thickness of the cast section is 200~230mm and the width is 900~1235mm.

[0032] It is understandable that appropriate thickness and width can ensure that the billet forms a uniform and solid shell during solidification, further reducing liquid level fluctuations.

[0033] Optionally, an automatic control system for the liquid level in the crystallizer is adopted, wherein the initial setting value of the KP system in the PID parameters is 1.0, and the initial setting value of the TI system is 0.5.

[0034] It is understandable that an appropriate KP (proportional gain) can reduce steady-state error and improve control accuracy. Increasing KP can improve the system's response speed, allowing the control system to react to deviations more quickly. However, an excessively large KP may lead to system instability and oscillations. Increasing TI (integral time) can eliminate the system's steady-state error and improve its steady-state accuracy. However, an excessively large TI may slow down the system response or even cause oscillations. Therefore, selecting appropriate PID parameters is crucial for stabilizing the liquid level. The inventors have discovered that by using the parameters defined above, liquid level fluctuations can be further reduced.

[0035] Furthermore, the depth of the immersion nozzle inserted into the liquid surface of the crystallizer is successively increased to 130mm-150mm-170mm.

[0036] When the nozzle is inserted too shallowly into the liquid surface of the crystallizer, the liquid surface in the crystallizer is prone to turbulence, which can further reduce the turbulence.

[0037] Specifically, the liquid level in the crystallizer is automatically controlled using an eddy current probe.

[0038] Please see Figure 3 In one specific embodiment, the control method provided by the present invention is implemented as follows: S1: When casting SPHC steel, the liquid level in the crystallizer 7 is detected by the eddy current probe 13, and the stopper rod 6 controls the steel flow to enter the crystallizer 7 through the submersible nozzle 9 for casting the billet.

[0039] S2: To ensure smooth casting and reduce the accumulation of inclusions 10 in the bowl of the upper nozzle 8, argon gas is blown into the upper nozzle 8 to form argon bubbles, causing the inclusions 10 accumulated in the bowl of the upper nozzle 8 to float to the surface. Similarly, inclusions 10 tend to accumulate on the inner wall of the submersible nozzle 9. Argon gas is blown into the stopper rod 6 through the stopper rod argon gas pipe 5 to blow off the inclusions 10. The flow rate control range of the upper nozzle argon gas 11 is 2.2-3.2 L / min, the flow rate control range of the stopper rod argon gas 12 is 1.0-2.5 L / min; the casting speed control range is 1.0-2.0 m / min, and the tundish temperature control range is 1550-1565℃.

[0040] S3: The cooling method for crystallizer 7 is weak cooling, with a speed of 3100L / min for the wide side and 460L / min for the narrow side; the secondary cooling is also weak cooling water meter, that is, the cooling intensity is 0.8L / kg.

[0041] S4: When the liquid level in crystallizer 7 fluctuates periodically, the secondary cooling weak cold water meter is switched to a secondary cooling SPHC dedicated water meter, i.e., the cooling intensity is 1.05L / kg, which reduces the periodic fluctuation of the actual liquid level in crystallizer 7 and ensures the stability of the liquid level.

[0042] The following is a detailed description of the control method for suppressing periodic fluctuations in the liquid level of the crystallizer in the production of SPHC steel provided by this invention, through specific experimental examples.

[0043] All the following experimental examples were conducted using the single-variable method. Specific process conditions were as follows: casting section thickness 200 mm, width 1235 mm, tundish temperature 1550-1565℃; crystallizer casting speed 1.4 m / min, amplitude 4.1 mm, frequency 161 Hz; crystallizer cooling water flow rate: 3100 L / min for the wide face and 460 L / min for the narrow face; secondary cooling intensity 1.0 L / kg; immersion nozzle insertion depth into the crystallizer liquid surface increased sequentially to 130 mm-150 mm-1... 70mm; the argon flow rate at the inlet is 2.7L / min, and the argon flow rate at the stopper rod is 1.5L / min; the initial setting value of the KP system in the PID parameters is 1.0, and the initial setting value of the TI system is 0.5; the mass composition of the low carbon steel protective slag includes: CaO: 30.35%, SiO2: 31.45%, Al2O3: 3.61%, F: 10.35%, Tc: 6.16%, MgO: 3.31%, basicity is 0.97, viscosity is 0.123Pa·s, and moisture content is 0.3%.

[0044] Experimental Example 1 In this experiment, all other process parameters remained unchanged. The effects of amplitude and frequency on the fluctuation of the liquid surface in the crystallizer were compared when the pulling speed was 1.0~2.0 m / min. The results are shown in Table 1.

[0045] Table 1 Speed amplitude Vibration frequency Negative slip time (s) Speed amplitude Vibration frequency Negative slip time (s) 1.0 3.5 165 0.146 1.0 2.5 175 0.137 1.1 3.7 164 0.146 1.1 2.6 174 0.138 1.2 3.8 163 0.147 1.2 2.7 173 0.139 1.3 4.0 162 0.148 1.3 2.8 172 0.140 1.4 4.1 161 0.149 1.4 2.9 171 0.140 1.5 4.3 160 0.150 1.5 3.0 170 0.141 1.6 4.4 159 0.151 1.6 3.1 169 0.142 1.7 4.6 158 0.152 1.7 3.2 168 0.143 1.8 4.7 157 0.153 1.8 3.3 167 0.144 1.9 4.9 156 0.154 1.9 3.4 166 0.145 2.0 5.0 155 0.155 2.0 3.5 165 0.145 Therefore, when the pulling speed is 1.0-2.0 m / min, the vibration amplitude of low carbon steel is 3.5-5.0 mm, the frequency is 165-155 times, and the negative slip time is controlled at 0.146-0.155 s. The negative slip time can be reduced by decreasing the amplitude and increasing the frequency. The amplitude is reduced by 1-1.5 mm and the frequency is increased by 10 times, which reduces the friction between the billet shell and the inner wall of the crystallizer, making the billet shell grow uniformly and smoothly, thereby reducing liquid surface fluctuations.

[0046] Experimental Example 2 In this experimental case, all other process conditions remained unchanged. The effects of secondary cooling on the liquid level fluctuation in the crystallizer were compared, and the results are shown in Table 2.

[0047] Table 2 steel grades Carbon content % Cooling intensity of secondary cooling treatment (L / kg) Periodic fluctuation value of liquid level in crystallizer (mm) Does the fluctuation of the liquid level in the crystallizer conform to a periodicity? The experiment aimed to determine whether it could alleviate the periodic fluctuations in the liquid level of the crystallizer. SPHC 0.038 0.8 13 conform to fluctuation SPHC 0.043 0.8 13 conform to fluctuation SPHC 0.046 1.05 1.5 conform to Stablize SPHC 0.045 1.05 No fluctuation conform to The liquid level remained stable without fluctuations. SPHC 0.041 1.05 No fluctuation conform to The liquid level remained stable without fluctuations. SPHC 0.040 1.05 No fluctuation conform to The liquid level remained stable without fluctuations. It is evident that, under the premise that other process parameters remain unchanged, when using the original weak secondary cooling water meter, the periodic fluctuation value of the crystallizer liquid level is around 13 mm. Increasing the secondary cooling intensity and using a dedicated SPHC water meter (i.e., a cooling intensity of 1.05 L / kg) significantly reduces the periodic fluctuation of the crystallizer liquid level, with the fluctuation value around 1.5 mm, or even zero. Experiments show that increasing the secondary cooling intensity thickens the billet shell in the secondary cooling zone, which can resist the outward impact force of the static pressure of molten steel on the billet shell under high casting speeds, thereby reducing billet bulging. This effectively alleviates the periodic fluctuation of the crystallizer liquid level, stabilizing the liquid level within ±3 mm or even eliminating fluctuations. The effect on reducing the periodic fluctuation of the crystallizer liquid level is significant, ensuring a stable crystallizer liquid level within the process requirement of ±3 mm.

[0048] Experimental Example 3 In this experiment, all other process conditions remained unchanged. The effect of the depth of the immersion nozzle inserted into the liquid surface of the crystallizer on the fluctuation of the liquid surface in the crystallizer was compared, and the results are shown in Table 3.

[0049] Table 3 steel grades Carbon content % Sprue insertion depth (mm) Periodic fluctuation value of liquid level in crystallizer (mm) Does the fluctuation of the liquid level in the crystallizer conform to a periodicity? The experiment aimed to determine whether it could alleviate the periodic fluctuations in the liquid level of the crystallizer. SPHC 0.038 Three courses 130 (130-150-170) 14 conform to fluctuation SPHC 0.043 Three courses 130 (130-150-170) 15 conform to fluctuation SPHC 0.046 Three courses for 150 (130-150-170) 11 conform to It has relieved SPHC 0.041 Three courses for 150 (130-150-170) 10 conform to It has relieved SPHC 0.040 Three courses 170 (130-150-170) 6 conform to It has relieved SPHC 0.037 Three courses 170 (130-150-170) 5 conform to It has relieved the symptoms. SPHC 0.044 Two 140 (140-160) 12 conform to fluctuation SPHC 0.046 Two 140 (140-160) 13 conform to fluctuation SPHC 0.043 Two 160s (140-160) 9 conform to It has relieved the symptoms. SPHC 0.040 Two 160s (140-160) 9 conform to It has relieved When the nozzle is inserted too shallowly into the liquid surface of the crystallizer, the liquid surface in the crystallizer is prone to turbulence, which can further reduce the turbulence.

[0050] Test Example 4 In this experimental example, all other process conditions remained unchanged. The effect of the argon flow rate at the inlet on the liquid level fluctuation in the crystallizer was compared, and the results are shown in Table 4.

[0051] Table 4 steel grades Carbon content Argon flow rate at the inlet (L / min) Periodic fluctuation value of liquid level in crystallizer (mm) Does the fluctuation of the liquid level in the crystallizer conform to a periodicity? The experiment aimed to determine whether it could alleviate the periodic fluctuations in the liquid level of the crystallizer. SPHC 0.049 2.7 7 conform to It has relieved the symptoms. SPHC 0.043 2.7 7 conform to It has relieved SPHC 0.051 1.7 10 conform to fluctuation SPHC 0.052 1.7 11 conform to fluctuation SPHC 0.044 2.2 9 conform to It has relieved the symptoms. SPHC 0.040 2.2 9.6 conform to It has relieved the symptoms. SPHC 0.040 3.2 7 conform to It has relieved the symptoms. SPHC 0.037 3.2 7 conform to It has relieved SPHC 0.045 3.7 11 conform to fluctuation SPHC 0.046 3.7 12 conform to fluctuation SPHC 0.044 4.2 12 conform to fluctuation SPHC 0.045 4.2 12 conform to fluctuation Experimental Example 5 In this experiment, all other process conditions remained unchanged. The effect of the stopper rod argon flow rate on the liquid level fluctuation in the crystallizer was compared, and the results are shown in Table 5.

[0052] Table 5 steel grades Carbon content % Argon flow rate (L / min) for stopper rod Periodic fluctuation value of liquid level in crystallizer (mm) Does the fluctuation of the liquid level in the crystallizer conform to a periodicity? The experiment aimed to determine whether it could alleviate the periodic fluctuations in the liquid level of the crystallizer. SPHC 0.038 1.5 10 conform to It has relieved SPHC 0.044 1.5 10 conform to It has relieved the symptoms. SPHC 0.039 1.0 12 conform to fluctuation SPHC 0.041 1.0 12 conform to fluctuation SPHC 0.042 2.0 9 conform to It has relieved SPHC 0.046 2.0 8 conform to It has relieved the symptoms. SPHC 0.041 2.5 8.5 conform to It has relieved SPHC 0.039 2.5 7 conform to It has relieved the symptoms. SPHC 0.044 3.0 14 conform to Slight fluctuations and steel turning SPHC 0.042 3.0 13 conform to Slight fluctuations and steel turning Experimental Example 6 In this experimental example, all other process conditions remained unchanged. The effects of the original KP value of the PID parameters on the liquid level fluctuation in the crystallizer were compared, and the results are shown in Table 6.

[0053] Table 6 steel grades Carbon content % PID parameter KP value in the crystallizer liquid level automatic control system Periodic fluctuation value of liquid level in crystallizer (mm) Does the fluctuation of the liquid level in the crystallizer conform to a periodicity? The experiment aimed to determine whether it could alleviate the periodic fluctuations in the liquid level of the crystallizer. SPHC 0.039 1.0 3 conform to It has relieved SPHC 0.040 1.0 3 conform to It has relieved the symptoms. SPHC 0.039 1.1 4.5 conform to It has relieved SPHC 0.043 1.1 4.5 conform to It has relieved the symptoms. SPHC 0.045 1.2 5 conform to It has relieved the symptoms. SPHC 0.043 1.2 5 conform to It has relieved the symptoms. SPHC 0.044 1.3 7 conform to It has relieved the symptoms. SPHC 0.034 1.3 7 conform to It has relieved SPHC 0.038 1.4 7.5 conform to It has relieved SPHC 0.035 1.4 8 conform to It has relieved the symptoms. SPHC 0.046 1.5 9 conform to It has relieved the symptoms. SPHC 0.042 1.5 9 conform to It has relieved the symptoms. Experimental Example 7 In this experimental example, all other process conditions remained unchanged. The effects of the original TI value of the PID parameters on the liquid level fluctuation in the crystallizer were compared, and the results are shown in Table 7.

[0054] Table 7 steel grades Carbon content % PID parameter TI value in crystallizer liquid level automatic control system Periodic fluctuation value of liquid level in crystallizer (mm) Does the fluctuation of the liquid level in the crystallizer conform to a periodicity? The experiment aimed to determine whether it could alleviate the periodic fluctuations in the liquid level of the crystallizer. SPHC 0.0439 0.5 4 conform to It has relieved the symptoms. SPHC 0.0465 0.5 4 conform to It has relieved the symptoms. SPHC 0.0521 0.6 5 conform to It has relieved the symptoms. SPHC 0.0416 0.6 5 conform to It has relieved the symptoms. SPHC 0.0401 0.7 6.5 conform to It has relieved the symptoms. SPHC 0.0426 0.7 6.5 conform to It has relieved the symptoms. SPHC 0.0439 0.8 7 conform to It has relieved the symptoms. SPHC 0.041 0.8 7.5 conform to It has relieved the symptoms. SPHC 0.044 0.9 8 conform to It has relieved the symptoms. SPHC 0.039 0.9 8 conform to It has relieved the symptoms. SPHC 0.047 1.0 10 conform to It has relieved the symptoms. SPHC 0.041 1.0 10 conform to It has relieved the symptoms. Experimental Example 8 In this experiment, all other process conditions remained unchanged. The effect of the pulling speed on the liquid level fluctuation in the crystallizer was compared, and the results are shown in Table 8.

[0055] Table 8 steel grades Carbon content % Pulling speed (m / min) Periodic fluctuation value of liquid level in crystallizer (mm) Does the fluctuation of the liquid level in the crystallizer conform to a periodicity? The experiment aimed to determine whether it could alleviate the periodic fluctuations in the liquid level of the crystallizer. SPHC 0.042 1.4 10 conform to It has relieved the symptoms. SPHC 0.042 1.4 10 conform to It has relieved the symptoms. SPHC 0.046 1.3 9 conform to It has relieved the symptoms. SPHC 0.050 1.3 9 conform to It has relieved the symptoms. SPHC 0.050 1.2 9.5 conform to It has relieved the symptoms. SPHC 0.036 1.2 9 conform to It has relieved the symptoms. SPHC 0.054 1.1 8.5 conform to It has relieved the symptoms. SPHC 0.055 1.1 8.5 conform to It has relieved the symptoms. SPHC 0.055 1.0 8 conform to It has relieved the symptoms. SPHC 0.046 1.0 7.5 conform to It has relieved the symptoms. SPHC 0.049 0.9 13 conform to fluctuation SPHC 0.046 0.9 12 conform to fluctuation SPHC 0.049 0.8 14 conform to fluctuation SPHC 0.043 0.8 14 conform to fluctuation SPHC 0.039 1.5 7 conform to It has relieved the symptoms. SPHC 0.036 1.5 7 conform to It has relieved the symptoms. SPHC 0.041 1.6 6 conform to It has relieved the symptoms. SPHC 0.044 1.6 6.5 conform to It has relieved the symptoms. SPHC 0.045 1.7 5 conform to It has relieved the symptoms. SPHC 0.039 1.7 5 conform to It has relieved the symptoms. SPHC 0.035 1.8 4 conform to It has relieved the symptoms. SPHC 0.049 1.8 4 conform to It has relieved the symptoms. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; if these modifications and variations fall within the scope of the claims of the present invention and their equivalents, they should all be considered to be within the protection scope of the present invention.

Claims

1. A method for controlling periodic fluctuations in the liquid level of a crystallizer during the production of SPHC steel, characterized in that, When casting SPHC steel, low-carbon steel protective slag is used, and the depth of the submerged nozzle inserted into the liquid surface of the crystallizer is 130~170mm; the casting speed of the crystallizer is 1.0-2.0m / min, the amplitude is 3~6mm, and the frequency is 170~150 times. This includes crystallizer cooling treatment and secondary cooling treatment; when the periodic fluctuation value of the crystallizer liquid level is ≤10mm, the cooling intensity of the secondary cooling treatment is 0.8~0.9L / kg; when the periodic fluctuation value of the crystallizer liquid level is >10mm, the cooling intensity of the secondary cooling treatment is 1.0~1.1L / kg.

2. The control method for suppressing periodic fluctuations in the liquid level of the crystallizer during the production of SPHC steel according to claim 1, characterized in that, The basicity of the low-carbon steel protective slag is 0.95±0.15, the viscosity is 0.2±0.1 Pa·S, and the moisture content is <0.5%.

3. The control method for suppressing periodic fluctuations in the liquid level of the crystallizer during the production of SPHC steel according to claim 1, characterized in that, The mass composition of the protective slag for low carbon steel includes: CaO: 28.5±5.0%, SiO2: 31.0±5.0%, Al2O3: 4.5±3.0%, F: 8.0±3.0%, Tc: 6.0±3.0%, MgO: ≤5.0%.

4. The control method for suppressing periodic fluctuations in the liquid level of the crystallizer during the production of SPHC steel according to claim 1, characterized in that, The intermediate temperature is 1550~1565℃, and the carbon content is ≤0.06%.

5. The control method for suppressing periodic fluctuations in the liquid level of the crystallizer during the production of SPHC steel according to claim 1, characterized in that, During the cooling process of the crystallizer, the water flow rate on the wide side is 3100~3300L / min, and the water flow rate on the narrow side is 460~500L / min.

6. The control method for suppressing periodic fluctuations in the liquid level of the crystallizer during the production of SPHC steel according to claim 1, characterized in that, The casting process is protected throughout. The argon flow rate at the top nozzle of the tundish is 2.2~3.2L / min, and the argon flow rate at the stopper rod is 1.0~2.5L / min.

7. The control method for suppressing periodic fluctuations in the liquid level of the crystallizer during the production of SPHC steel according to claim 1, characterized in that, The thickness of the cast section is 200~230mm, and the width is 900~1235mm.

8. The control method for suppressing periodic fluctuations in the liquid level of the crystallizer during the production of SPHC steel according to claim 1, characterized in that, An automatic control system for the liquid level in the crystallizer is adopted, wherein the initial setting value of the KP system in the PID parameters is 1.0, and the initial setting value of the TI system is 0.

5.

9. The control method for suppressing periodic fluctuations in the liquid level of the crystallizer during the production of SPHC steel according to claim 1, characterized in that, The depth of the immersion nozzle inserted into the liquid surface of the crystallizer is successively increased to 130mm-150mm-170mm.

10. The control method for suppressing periodic fluctuations in the liquid level of the crystallizer during the production of SPHC steel according to any one of claims 1-9, characterized in that, The liquid level in the crystallizer is automatically controlled using an eddy current probe.

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